This invention relates to a tire belt folding apparatus for use in the preparation of belts, which are used in the manufacture of radial pneumatic tires.
As is well known in the art, the radial tire has a circumferentially extending tread portion, a belt underneath the tread portion, and sidewalls which are continuous at either side of the crown of the tire having laterally and downwardly extending portions. Beneath the belt and sidewall portions is the carcass of the tire constituting the body that imparts additional strength to the tire made up of a plurality of layers or plies of superimposed rubberized tire fabric that adheres firmly to each other and to the outer rubber covering during the vulcanization process.
The fabric for the belts and the plies is made up of a multiplicity of adjacent cords which, when initially made have the cord in parallel side-by-side relationship with a thin friction coat of rubber stock thereon and therebetween. The stock is cut on a bias to provide strips of fabric wherein the cords run from one side of the fabric piece to the other on a bias at a predetermined angle. The bias cut fabric material is spliced to provide a longitudinally extending ply stock material that can be used as belt material or as tire carcass material or ply stock wherein the bias-cut fabric is laid on the tire building drum for buildup of the green tire in cooperation with inextensible beads, and other ply stock including tread and sidewall rubber in a manner old and well known in the art. Accordingly, when fabricating a belt from bias-cut fabric care must be used in handling the belt fabric since it is important to maintain exact dimensions and control of the belt width.
The belt can be one or more layers designed to include folded plies with the edges thereof located along the shoulder of the tires or along the lateral edges of the tread portions. One particular problem with the use of belts is belt edge separation. Belt edge separation is the tendencies of the cut edges of the belt plies to pull away or separate from the other portions of the tire carcass, or from adjacent belt plies. Such belt edge separation adversely affects the tires reliability and durability. In order to improve tire performance an apparatus has been designed to receive belt material whose width is greater than the specifications that the tire requires, wherein the tire material is then folded regardless of width variations to provide an exact control on belt width dimensions while improving the characteristics of the respective lateral circumferential edges of the belt. The variation in width of material is automatically absorbed in that portion folded over. Two overlapping folded belts with their folded edges located on the respective lateral sides of the tire tread allow minimum distortion, with no pull down in belt width and angle. The apparatus for fabricating such belts is capable of folding rayon, fiberglass or wire materials. In the unique folding operation, the stitching done permits the continuous length of folded belt to be precisely cut or torn at the precise bias angle to the exact dimensions at the tire building machine.